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A. Field of the Invention
The present invention relates to the field of data communications, and more particularly to the field of communicating digital data between a wireless user and a computer network.
B. Background of the Invention
Network access servers that provide local or wide area network access for remote users dialing in over the public switched telephone network are known in the art. These devices are available from 3Com Corporation, the assignee of the present invention. The Total Control Network Enterprise Hub from 3Com is a representative network access server. It is described in U.S. Pat. No. 5,577,105 of Baum et al., entitled xe2x80x9cTelephone Call Switching and Routing Techniques for Data Communications,xe2x80x9d and U.S. Pat. No. 5,528,595 of Walsh et al., entitled xe2x80x9cModem Input/Output Signal Processing Techniques.xe2x80x9d The Walsh et al. and Baum et al. patents are both fully incorporated by reference herein.
The network access server described in the Walsh et al. and Baum et al. patents provides an interface to a multiplexed digital telephone line, a plurality of modems for performing signal conversions for the data from the remote users, and a network interface for transmitting demodulated data from the modems onto a local or wide area network. A high speed midplane bus structure comprising a time division multiplexed bus provides a signal path between the channels of the telephone line and the modems. The high speed midplane also includes a parallel bus that couples the modems to the network interface.
This network access server architecture in a single chassis has proven to be very popular in a variety of applications, particularly corporate network access. The network access server is also particularly popular with Internet service providers for land-based Internet users. With a single network access server, the Internet service provider can handle a large number of simultaneous Internet access calls and provide full duplex communication between the multiple remote users and host computers on the Internet.
The technology for Internet access for wireless users is now emerging. There are two competing standards for wireless service, CDMA (Code Division Multiple Access, described in the standard documents IS-130 and IS-135, incorporated by reference herein) and TDMA (Time Division Multiple Access, described in standards document IS-99, also incorporated by reference herein). These standards specify standards and guidelines for digital wireless communications for both voice and data. The two standards differ in how digital data from multiple users are multiplexed on the radio interface.
In accordance with both wireless technologies, a wireless user transmits data to a mobile switching center. The mobile switching center provides connectivity to the public switched telephone network, certain multiplexing and control function, and switching functions for the wireless users. Multiplexed digital data from a plurality of remote wireless users is then capable of being transmitted via high-speed communication formats (such as Frame Relay) to communication elements in the public switched telephone network.
The mobile switch center may also be connected to a network access server to provide Internet access and corporate network access to wireless users over a wireless link. The network access server provides for the functions needed for terminal equipment connected to a TDMA or CDMA mobile telephone to inter-work with terminal equipment connected to the public switched telephone network and the Internet.
The mobile switch centers provide buffers to store digital data that is to be multiplexed for distribution to the wireless users via a plurality of base stations. The mobile switch centers currently available on the digital wireless telephone system were originally designed for voice communication through telephone handsets. The volume of signal exchanged between handsets may not require extensive buffering along the signal path. However, a data network communicating via high-speed links may transmit a large amount of digital data to wireless users. The buffers in the mobile switch center, which have been designed to communicate voice signals, may not have the capacity to store the digital data sent from the data network. This may result in overflow and the loss of data.
Connections to the data network that use the Transport Control Protocol (TCP) include a built-in flow control mechanism that may alleviate some buffer overflow. The TCP flow control mechanism uses a TCP receiving window in the mobile device to control the flow of data received. If the receiving window is larger than the buffer in the mobile switch center, the TCP flow control mechanism is useless.
It would be desirable to control the flow of data to a wireless user from a data network to prevent buffer overflows in the mobile switch center.
In view of the above, a system is provided for controlling data flow to a wireless user over a wireless network. The system includes an inter-working gateway connected to a data network. The inter-working gateway receives a plurality of network data transmissions having a network data size from the data network for sending to the wireless user. The system includes a switch center connected to the inter-working gateway. The switch center receives a plurality of gateway data transmissions having a gateway data size from the inter-working gateway for sending to the wireless user. The switch center includes a switch buffer for storing data from the plurality of gateway data transmissions. The switch buffer has a switch buffer size. A wireless link is included for communicating a plurality of switch data transmissions, each having a switch data size, between the wireless user and the switch center. A data flow controller in the inter-working gateway controls the gateway data size of the gateway data transmissions by determining an available buffer size in the switch buffer. The gateway data size is less than or equal to the available buffer size.
In another aspect of the present invention, an improved network access server is provided for connecting to a data network and to a mobile switch center in a wireless network. The switch center is connected to at least one wireless user via a wireless link. The network access server receives a network data transmission from the data network and sends a gateway data transmission to the switch center. The switch center receives the plurality of gateway data transmissions and sends a plurality of switch data transmissions to the wireless user. The wireless link transmits data at an airlink data rate. The mobile switch center includes a switch buffer for storing the switch data transmissions being sent to the wireless user. The switch buffer has a switch buffer size.
The improvement to the network access server includes a data flow controller for determining a gateway data size of the gateway data transmissions that it sends to the switch center. The data flow controller determines the gateway data size by determining an available buffer size in the switch buffer. The data flow controller ensures that the switch data size is less than or equal to the available buffer size.
In yet another aspect of the present invention, a method is provided for controlling the data flow between a switch center and a wireless user in a wireless network that receives data from a data network. According to the method, a plurality of network data transmissions is received at an inter-working gateway. A gateway data size is determined for transmitting a gateway data transmission. The gateway data size is determined by determining an available buffer size for a switch buffer in the switch center. The gateway data size is less than or equal to the available buffer size. The gateway data transmission of the gateway data size is then sent to the switch center. The available buffer size is periodically adjusted.